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"Influence of Viscoelasticity on the Atomization of Polymer Solutions" Yenny Christanti (Advisor: Lynn M. Walker, Dept. Chemical Engineering) There are many applications involving atomization of viscoelastic fluids (paints, coatings, inks, jet fuels, etc.). The presence of polymers in these fluids induces viscoelasticity and changes the spray characteristics. Despite this wide-range of applications, the break up of viscoelastic fluids is not understood. However, it has been suggested that the key viscoelastic property is the extensional behavior. How much
effect does viscoelasticity have on sprays?
Fluid A and B have the same shear viscosity, surface tension, and density. The difference in the spray characteristics is due to the difference in the extensional behavior. Fluid B is a strain-hardening fluid (polymer solution) while Fluid A is Newtonian. Approach: The break up of a jet into drops is not only directly applicable to processes such as ink jet printing and particle production, but is also an important step in atomization, which is more complex but involves the same physics. We are currently investigating the relationship between viscoelasticity and drop formation aimed at the production of monodisperse colloidal sized droplets. For Newtonian fluids, the final break up occurs through jet pinching which is influenced by the bulk properties of the fluid, namely viscosity, surface tension, and density. The addition of highly extensible polymer molecules changes the rheology of the bulk fluid influencing interfacial break up. To probe the effect of viscoelasticity on the drop formation, we use a series of model fluids which have the same shear viscosity, surface tension, and density. Any change in the break up is due to viscoelasticity of the fluids. The effect of increasing viscoelasticity on drop formation:
For Newtonian fluids, the final break up occurs through jet pinching which is influenced by the bulk properties of the fluid, namely viscosity, surface tension, and density. The addition of highly extensible polymer molecules changes the rheology of the bulk fluid influencing interfacial break up. In addition to viscous stress, elastic stress induced by the presence of macromolecules balances the interfacial stress. Viscoelasticity retards the formation of satellite drops. Capillary pressure causes fluid to drain from the filaments into the beads, but the relaxation time of the fluid dictates the draining rate. PUBLICATIONS & PRESENTATIONS
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